1. Field of the Invention
The present invention generally relates to a sensor device and a stage device, and more particularly to a sensor device which is adapted to detect the state of a stage which is moved with high accuracy, and a stage device in which the sensor device is provided.
2. Description of the Related Art
Concerning ultra-precision machining devices and semiconductor devices which are the basis of information processing technology, the demand for high-accuracy positioning and high-speed processing of stage devices, used for these devices, is increasing. For example, for the stage device which is a key component of a semiconductor exposure device, the positioning accuracy on the order of 10 nm and the movement range of several hundreds of millimeter are needed. For this reason, it is necessary to measure precisely the multiple degree of freedom position and attitude of the stage, to feed back the measurement results, and to perform positioning control of the stage.
Generally, as a position instrumentation system of a conventional positioning device, an optical linear encoder, a laser measuring machine, an autocollimator, etc. have been used. These devices fundamentally use as the basic principle one-dimensional length or attitude measurement, and perform instrumentation of the position or the attitude with the combinations of the one-dimensional length or attitude along each of a plurality of axes.
In a laser interferometer used for high precision instrumentation, in order to measure the position of the stage (positioning object) using a laser beam, there is a problem that the accuracy of a measurement value falls by a fluctuation of the air in the device in which the stage is placed.
In a laser interferometer, the optical components can be disposed only on the exterior of the stage, in order to prevent the fluctuation of the air, it is necessary to arrange the metallic pipe which serves as an optical path of a laser beam for every direction. For this reason, there is the problem in that the whole stage device is enlarged in size and the structure becomes complicated.
In rotating the stage around the Z-axis, there is a problem in that the reflected light from the stage separates from the light receiving unit of the interferometer and the X-Y direction position detection becomes impossible.
A sensor device which is adapted to solve such problems is known. In the known sensor device, a reference grating is irradiated by a laser beam, and the two-dimensional angles of the X and Y directions of the reflected light reflected by the reference grating (angle grating) are detected by a two-dimensional angle sensor.
FIG. 1 is a schematic diagram showing a sensor device which has a reference grating and a two-dimensional angle sensor.
As shown in FIG. 1, in this sensor device 300, the position in the X/Y direction is detected based on a change of the output signal of a two-dimensional angle sensor 290.
The two-dimensional angle sensor 290 is adapted to detect the inclination of the surface of a reference grating 320, and to detect a change of the direction of a line normal to the surface of the reference grating 320. Therefore, the inclination of the XY direction (two-dimensional) and the change of the normal line can be detected by using the two-dimensional angle sensor 290.
The reference grating 320 has a configuration, composed of crests and troughs collectively, which is varied periodically in accordance with a known function, in the two orthogonal directions (the X-direction and the Y-direction) on the flat surface. For example, a sinusoidal waveform is used for the configuration of the reference grating 320.
Next, the two-dimensional angle sensor 290 shown in FIG. 1 will be explained with reference to FIG. 2. FIG. 2 shows the composition of a two-dimensional angle sensor.
The two-dimensional angle sensor 290 is a geometrical-optics sensor based on the auto-collimation method. As shown in FIG. 2, a laser beam 310 emitted by a laser light source 301 passes through a polarization beam splitter 302 and a ¼ wavelength plate 303, and enters into the surface of the reference grating 320.
A laser beam 312 reflected on the surface of the reference grating 320 is reflected by the polarization beam splitter 302, and the resulting laser beam 312 enters into an autocollimator 305. The autocollimator 305 comprises an objective lens 306, and a photodetector 307 which detects the position of a spot formed by the incident laser beam.
In the above-mentioned auto-collimation method, an image of a target plate (which is usually a cross line) at the focal point of the objective lens 306 is formed at the infinitely distant point, and a parallel light reflected by a plane mirror at a subsequent position from the objective lens 306 is converged at the conjugate position of the target plate surface, and it is necessary to read out a minute angular displacement of the plane mirror from the displacement of the converged image of the cross line within the mirror surface.
For this reason, the auto-collimation method requires the use of an expensive and complicated component, such as the autocollimator 305, and there is a problem that the cost of sensor device 300 becomes high.
In addition, the position detection is performed with high resolution, and there is a possibility that the geometrical-optics principle may not be satisfied due to interference and diffraction of the light as the period of the reference grating 320 and the multi-spot becomes short. For this reason, there is a problem that it is difficult to detect with sufficient accuracy.
In order to detect the state of five degrees of freedom of a movable stage including two-dimensional displacements (X-direction and Y-direction displacements), and three attitude changes (rotation angle around the X-axis, rotation angle around the Y-axis, and rotation angle around the Z-axis), the auto-collimation method requires the use of three two-dimensional angle sensors 300. Therefore, there is a problem that the adjustment between these sensors is difficult to perform.
In the stage device, while the position detection is performed when moving the stage, the drive control of a pair of linear motors provided on both the sides of the stage is performed. In order to raise the position detecting accuracy at this time, it is necessary to make the above-mentioned sensor device 300 in a simple arrangement and detect accurately the movement amount and the inclination of the linear motor.
As another sensor device, a linear scale is known. In the known linear scale, a slit plate is formed to extend in the moving direction of the stage, and the number of slits in the slit plate is optically detected by using an optical sensor which is moved relative to the slit plate, so that the position of the stage is detected.
By using this linear scale, the amount of displacement of the stage in the moving direction can be detected. However, the amount of displacement of the stage in a different direction than the moving direction (for example, the up/down direction displacement and inclination angle around each axis of the stage) cannot be undetected by using the linear scale.
Therefore, in the conventional stage device, a pair of linear scales are further arranged on both sides of the stage, and the yawing angle of the stage is determined through the computation based on the difference between detection signals detected by the pair of linear scales. And movement of the stage is controlled, without detecting the inclination angles of the stage in the other directions than the moving direction.
In the conventional stage device, the drive control of the linear motors is performed based on the position (movement amount) of the stage in the moving direction acquired from the linear scales, and monitoring correctly the inclination state in the other directions cannot be performed when moving the stage.
For this reason, there is a problem in that, if the stage is inclined, it is difficult to detect correctly the amount of the inclination of the stage and it is difficult to check in which direction the stage is inclined.